LATE PALEOZOIC SUTURING/UNZIPPING OF GONDWANA—LAURENTIA [PANGAEA]: INSIGHTS FROM THE ARBUCKLE MOUNTAINS OF SOUTH-CENTRAL OKLAHOMA

During late Carboniferous–Permian time, the rift-bounded Precambrian core of ancestral North America [i.e. southern Laurentia] was attached to Gondwana along a dextral-transpressional plate boundary [e.g. Mueller et al. 2014]. Oblique suturing of supercontinental landmasses—Laurentia/Gondwana—predicts age-equivalent right-lateral transcurrent faulting and map-scale folding [cf. Sanderson and Marchini 1984] in the Ouachita orogen of southern Oklahoma. However, right-oblique convergence is incompatible with sinistral-transtension and extensional deformation in the Arbuckle Mountains; our photo-essay explains why. In situ field photographs shot along a NS transect through 1:100,000-scale map of Ham et al. [1954]:

1. SW-dipping strata on upright limb of major NE-vergent anticline.

2. Sinistral-transtension recorded by shallow E-plunging slickenlines.

3. Pebble-cobble conglomerate attesting to uplift/erosion/deposition.

4. Students take 20-second time-out to discuss geology of fried pies.

5. Fossil-rich beds in footwall of minor thrust fault: critters unscathed.

6. Down-stepping on slickenside records evidence of normal faulting.

7. Asymmetric fold [z-shape] suggests tectonic transport to the south.

8. SW-dipping strata approaching hinge zone of overturned anticline.

9. Asymmetric fold [s-shape] suggests tectonic transport to the north.

10. Brittle fault zone crosscuts 2nd-order folds on map-scale anticline.

11. Plumose structure documenting local mode-I fracture propagation.

12. Calcite slickenfiber growth records hanging wall down movement.

While structures documenting ~NS compression/supercontinental suturing[?] were identified [bivergent tight-to-isoclinal folds, minor thrusts; field photographs #1, 5, 7, 8, and 9], extensional deformation was also recognized as evidenced by overprinting brittle normal faults [mineralized surfaces; photographs #6, 12] and opening mode fracture arrays [fractographic markings, photo #11]. Late extensional and sinistral-transtensional deformation [photos #2, 4] are possibly explained by gravitational collapse [i.e. 'unzipping'] of the Ouachita contractional orogen following late Paleozoic uplift/erosion [photo #3; synorogenic clastic sedimentation] and assembly of the Pangaean landmass.